These investigations will attempt to elucidate the pathogenesis of viral infections of the adult and fetus using immunological and virological techniques. Herpes simplex virus, CMV, and varicella have been agents which have received particular attention in these studies, since they have significant neurotropic capabilities in terms of newborn and adult encephalitides. There is considerable speculation that these viruses may have latent, "slow" virus potential in relationship to chronic diseases of humans, including carcinoma and central nervous system infection. The effects of PML, SV40, BK virus infection will be studied in the owl monkey.